NAIADACE^E. (PONDWEED FAMILY.) 433 



ing of single ovate or oval 1-celled sessile anthers, as large as the ovaries, and 

 containing a tuft of threads in place of ordinary pollen : the fertile of single 

 ovate-oblong ovaries attached near their apex, tapering upward into an awl- 

 shaped style, and containing a pendulous orthotropous ovule : stigmas 2, long 

 and bristle-form, deciduous. Utricle bursting irregularly, enclosing an oblong 

 longitudinally ribbed seed (or nutlet). Embryo short and thick (proper cotyle- 

 don almost obsolete), with an open chink or cleft its whole length, from which 

 protrudes a doubly curved slender plumule. Grass-like marine herbs, growing 

 wholly under water, with a jointed creeping stem or rootstock, sheathed by the 

 bases of the very long and linear, obtuse, entire, grass-like, ribbon-shaped leaves 

 (whence the name, from ^oaor^p, a band). 



1. Z. imil'iim, L. Leaves obscurely 3-5-ncrved. Common in bays 

 along the coast; in water of 5 -15 deep. Aug. (Eu.) 



4. RIJPPIA, L. DITCH-GRASS. 



Flowers perfect, 2 or more approximated on a slender spadix, which is at 

 first enclosed in the sheathing spathe-like base of a leaf, naked (entirely desti- 

 tute of floral envelopes), consisting of 2 sessile stamens, each with 2 large and 

 separate anther-cells and 4 small sessile ovaries, with a single campylotropous 

 suspended ovule : stigma sessile, depressed. Fruit of little obliquely-ovate 

 pointed drupes, each raised on a slender stalk which appears after flowering; 

 the spadix itself also then raised on an elongated thread-fonn peduncle. Em- 

 bryo ovoid, with a short and pointed plumule from the upper end, by the side 

 of the short cotyledon. Marine herbs, growing under water, with long and 

 thread-like forking stems, slender and almost capillary alternate leaves with a 

 dilated sheathing base. Flowers rising to the surface at the time of expansion. 

 (Dedicated to Rappias, a German botanical author of the early part of the 18th 

 century. ) 



1. K. limr^tifiiia, L. Leaves linear-capillary ; nut ovate, obliquely 

 erect; fruiting peduncles capillary ('-!' long). Shallow bays, along the 

 whole coast : chiefly a narrowly leaved variety with strouglv pointed fruit, ap- 

 proaching R. rostellata, Koch. June -Aug. (Eu.) 



5. POTAMOGETON, Tourn. POXDWEED. 



Flowers perfect, spiked. Sepals 4, rounded, valvate in the bud. Stamens 4, 

 nearly sessile, opposite the sepals : anthers 2-cclled. Ovaries 4 (rarely only 

 one), with an ascending campylotropous ovule : stigma sessile or on a short 

 style. Nutlets drupe-like when fresh, more or less compressed. Seed curved 

 or cochleate ; the radicular end of the embryo pointing downwards. Herbs 

 of fresh or barely brackish ponds and streams, with jointed creeping and root- 

 ing stems, and 2-ranked pellucid leaves, which are usually alternate or imper- 

 fectly opposite ; the upper sometimes dilated, of a firmer texture, ani floating. 

 Stipules membranous, more or less united and sheathing. Spikes sheathed 

 by the stipules in the bud, raised on a peduncle to the surface of the water. 

 (An ancient name, composed of Trora/ios, a river, and yeirajp, a neighbor, from 

 their place of growth.) 



37 



